You have to respect the distance recommendations that are made by the manufacturer, and some MVBs are putting out either too much or too little UVB. But not all MVBs are alike. There are good ones and bad ones just as there are good and bad florescent bulbs, and some other really bad uvb bulbs.
The recommended distance that you should keep your basking spot away from the bulb is 19 inches if you use a Megaray. If you let your lizard sit 5 inches from the bulb, yes, it will cause problems for the lizard. If you use a tight beam bulb like a Megaray or a T Rex, then you are not in danger of exposure unless you hang out in your lizard viv.
I have been keeping lizards under Megarays and T Rex Active UV MVB bulbs for a few years now, and I'm not green or riddled with cancer, my lizards are disgustingly healthy, and none of us are blind.
In fact, the only blind lizard that I have was kept under a COIL florescent before she came to me as a rehab. I have some of the heathiest lizards you'll find in captivity. GOOD MVBs used correctly produce better UVB than the best florescent for 3 times as long, and will not harm you or your reptiles, IMO. Here is where I get mine and there is good reading n the subject here as well.
www.reptileuv.com